The present invention relates generally to pressure regulating devices and, more particularly, to pressure regulating devices for fuel systems.
To help meet consumer demand for more fuel efficient vehicles, automotive companies have begun investigating the use of direct injection fuel systems for internal combustion engines. In a direct injection fuel system, a fuel injector injects highly pressurized fuel directly into an engine cylinder combustion chamber during the compression stroke. Direct fuel injection can facilitate efficient fuel combustion, thereby improving fuel economy.
Because fuel is injected during a compression stroke, the fuel must be at a high pressure (e.g., about 200 Bar or 2,900 psi) in order to enter the cylinder. High fuel pressure is typically achieved by using a high-pressure booster pump in conjunction with a low pressure fuel tank pump.
FIG. 1 is a schematic illustration of a conventional direct injection fuel system 5 for an internal combustion engine. Fuel, such as gasoline, is pumped from a tank 10 via a low pressure tank pump 12 to a high pressure booster pump 14. The high pressure booster pump 14 raises the pressure of the fuel so that the fuel can enter a combustion chamber against the compression pressure in the cylinder. Typically, a high pressure booster pump is mounted to an engine and is operated directly from a cam (or crank) shaft within the engine. As illustrated in FIG. 1, the high pressure fuel discharged from the high pressure booster pump 14 flows through a fuel rail 42 and to each injector 18 via a respective fuel passageway 20. Each injector 18 is configured to deliver a controlled amount of fuel into a respective cylinder 22 when activated by an engine control unit (ECU) 24. Conventionally, fuel pressure in a fuel rail 42 is controlled via a fuel rail pressure regulator 26 and a fuel rail pressure sensor 28. Typically, the pressure sensor 28 and pressure regulator 26 communicate with each other via an ECU 24.
Because two separate components (i.e., a pressure regulator and a pressure sensor) are typically used to control fuel pressure in conventional direct injection fuel systems, multiple connections in a fuel rail are typically necessary. Unfortunately, each connection in a high pressure fuel rail is a potential source of fuel leakage. Because fuel rails are typically mounted near hot exhaust manifolds, the potential for fire caused by a fuel leak from a high pressure fuel rail can be substantial.
In view of the above discussion, it is an object of the present invention to facilitate reducing the potential for fire caused by fuel leaks in high pressure direct injection fuel systems for internal combustion engines.
It is another object of the present invention to provide fuel pressure monitoring and control for high pressure direct injection fuel systems wherein only a single connection in a fuel rail is required.
These and other objects of the present invention are provided by pressure regulating devices for high pressure fluid systems, such as fuel systems, wherein a pressure sensing element is attached directly to a pressure chamber within a pressure regulating device. According to one embodiment of the present invention, a sense tube assembly is disposed within an axial bore of a housing. The sense tube assembly includes a longitudinally extending outer tube having a longitudinally extending inner tube disposed within the outer tube to define a fuel pressure chamber.
The outer tube has a tubular body terminating at an open end and at an opposite closed end. A longitudinally extending channel is formed along the inner surface of the outer tube body from the outer tube open end toward the outer tube closed end.
The inner tube has a tubular body terminating at an open end and at an opposite closed end. The inner tube closed end includes an aperture formed therethrough. A radially extending flange is positioned adjacent the inner tube open end and has an aperture formed through a portion thereof. The longitudinally extending channel in the outer tube is in fluid communication with a fuel inlet passageway in the housing via the flange aperture. The longitudinally extending channel in the outer tube forms a fuel flow path between the inner tube and the outer tube from the fuel inlet passageway to the fuel pressure chamber.
A magnetic pole piece is disposed within the inner tube and includes opposite first and second ends and an internal bore that terminates at the magnetic pole piece first and second ends. The magnetic pole piece internal bore is in fluid communication with a fuel outlet passageway in the housing.
A magnetic armature is slidably secured within the inner tube between the magnetic pole piece and the inner tube closed end. The magnetic armature includes a body having a pair of slots formed in the outer surface thereof and terminating at opposite first and second ends. The magnetic armature second end is configured to matingly engage the aperture in the inner tube closed end. The slots formed in the armature are in fluid communication with the magnetic pole piece internal bore. A spring, located between the magnetic armature and magnetic pole piece, is configured to bias the magnetic armature away from the magnetic pole piece and to cause the magnetic armature second end to matingly engage the aperture in the inner tube closed end.
A pressure sensing element is attached to the outer tube closed end and is configured to measure fuel pressure within the pressure chamber. The pressure sensing element includes a semiconductor element that deflects in response to a deflection of the outer tube second end caused by pressure within the pressure chamber. A coil disposed within the housing is electrically connected with the pressure sensing element and is configured to generate a magnetic field responsive to electrical signals from the pressure sensing element. The magnetic field moves the magnetic armature axially within the inner tube to control fuel pressure by allowing fuel entering-the pressure chamber via the fuel inlet passageway to exit via a fuel outlet passageway.
Because the present invention combines a pressure sensing element and pressure regulator within a single device, only a single connection in a fuel rail is required. Accordingly, the number of potential sources of fuel leaks is reduced by the present invention.
According to another embodiment of the present invention, a controller, such as a proportional-integral-derivative (PID) controller, may be electrically connected with the pressure sensing element to create a xe2x80x9csmart solenoidxe2x80x9d whereby fuel pressure can be maintained within a prescribed range of pressures. The controller closes the loop around the sensed pressure via the pressure sensing element and adjusts the voltage to the coil which controls the axial movement of the magnetic armature within the inner tube in order to maintain fuel pressure within a predetermined range.
According to another embodiment of the present invention, a post-assembly calibration method is provided to compensate for mechanical strain imposed on pressure sensing elements during assembly of pressure regulating devices. A pressure sensing element attached to a pressure chamber within a pressure regulating device housing is electrically connected to an electrical terminal located external to the housing. The pressure sensing element is then calibrated to compensate for mechanical strain imposed on the pressure sensing element during assembly by transmitting electrical signals to the pressure sensing element via the electrical terminal.
The present invention may be utilized with various high pressure fluid systems, and is not limited to high pressure fuel systems.